Furnace



Feb. 21, 1933. LT. G. CCGHLAN ET AL FURNAE Filed July 21, 19

25 4 Sheets-Sheet- 2 llllll' EN TORS @mgl FebQ2.1,"1933.v

T. G. c'oGHLAN ET Al. 1,898,479

FURNACE Filed July 21, 1925 4 sheets-sheet s Feb. 2l, 193.3. T. G. coGHLAN ET AL FURNACE Filed July 21, 1925 4 Sheets-Sheet 4 240mg @'INVENToRS QZ?" 4, M

ATT ORNEYS Patented Feb. 2l, 1933 UNITED STATES PATENT OFFICE THOMAS G. COGHLAN, OF- ELIZABETH, AND

NEW JERSEY; SIG-RID A. JOHNSEN EXECUTRIX F SAID EINAR A. JOHNSEN,

DECEASED FURNA-.CE

Application led July 21,

. methods for operating such furnaces, and

will be best understood from the following. description and the annexed drawings of an illustrative embodiment of our invention and of an apparatus by carried out' In the drawings, Fig. 1 is a vertical longitudinal section of the illustrative embodiment; Fig. 2 is a modification of-a part of Fig. 1; Fig. 3 is a side View, more or lessl diagrammatic, of the boiler and furnace of Fig. l, on a smaller scale, showing the exterior combustionl air supply system; Fig. Lisa plan View, partly in section, on the line 4-4 of Fig. 1; Fig. 5 is an enlarged view of a portion of Fig. 1; Fig. 6 is a front view of one which our method may be of the details of Fig. 5; Fig. Y7 is an enlargement of a portion of Fig. l, and Fig. 8 is' a section on the line 8 8 of Fig. 7. y

Like reference characters indicate like i parts throughout the drawings.

In the illustrativeembodiment, the steam boiler which we have chosen for purposes of illustration, is provided with water tubes 10,

vuptake headers 11, downtake headers 12 and `a steam and water drum 13,'all connected `in the usual manner. 'Baiies 14 and 15-direct the gases entering at the bottom of the iir'st pass adjacent the uptake headers, back and forth across the water tubes to the gas exit 16.

As shown best in Fig. 1, the furnace is formed so as to have upper and lower combustion chambers connected by a restricted passage. In the lower part of the furnace is means to burn fuel, exemplified by a chain grate stoker 17 which receives its fuel from the hopper 18 and carries it to the right of Fig. 1, the ashes being deposited in the usual ash hopper through the opening 19.

At the front of the Stoker 17 are a' pair of curved arches 20 and 21, the latter projecting over the forward part of the grate to form a combustion arch therefor. Similarly, at the rear of the chain grate stolzer 17 is an arch 22 and an arch 23, the latter also forming a combustion arch or roof extending well forwardly over the rear end of the Stoker, 'the is best shown in Fig. 3,

1925. Seriall No. 44,957.

arches 21` and 23 together forming the roof of the combustion chamber. The inner ends of the arches 21 and 23 are curvedso as to provide a narrow passage or throat 24 into which the gases from the lower chamber are directed by the arches 21 and 23.

The` passage 24 merges into an upper combustion chamber 25 which preferably is provided with walls diverging upwardly and outwardly from the passage 24, the chamber 25 preferably having an upper boundary vformedin part by the flat roof 26 and in part by the lowermost tubes of the boiler, these tubes being disposed over the passage 27 of the chamber 25 and thus being exposed to the hot gases in that part of the chamber 25. From the passage 27 ofthe chamber 25, the hot gases How upwardly into the first pass of the boiler.

of the passage 24 at its most restricted point v is preferably not more than seventeen percent of the effective length of the Stoker in the furnace, i. e., the length of the Stoker area through which air is passed.

AAt each side of the widened part of the narrow air inlets arranged to direct the air crosswise of the passage. The illustrative arrangement of these inlets is best shown in Figs. 5 and 6. A series of tuyres or nozzles 28 extend across the furnace side by side, the rear end of'each of the nozzles communicating with an air duct 29 or 30, as the case may be, formed, in the illustrative arrangement, of a pair of I-beams 31 covered by plates 32, the rear ends of the nozzles 28 extending through the I-beams to communicate with the air duct. The beams 31 not only form the air ducts, but also support the walls of the combustion chamber 25. Preferably the nozzles are formed as shown best in and narrow mouth 33.

The combustion air supply for the furnace in which an air heater' 34 of any ofthe wellknown types heats the combustion air entering the air heater through the duct 35 l the duct 36 toand through the fan 37'and' a-feed water heater or economizer intoa ENAR A. JOHNSEN, 0F MOUNTAIN LAKES,

passage 24 are auxiliary combustion Fig. 5, with a long and then flows through 1 As illustrated in the drawings, the len h 70 duct 38 which communicates with spaces along the stoker 17 and between the runs thereof to supply the usual combustion air flowing through the fuel on the grate. From the fan 87 leads also a duct 39 which communicates with the ends of each of the ducts 29 and 30 from which the air flows through the nozzles 29 into the narrow passage 24. Dampers in the several ducts are provided so that the amount of air delivered to any part of the furnace can be controlled.

Vith the arrangement described, the furnace is preferably operated as follows:

Air is supplied through the duct 38 at pressures insufficient to lift the heavier particles of the fuel from the bed, but in sufficient quantities to burn the solid fuel on the grate. The amo'unt supplied, however, is insufficient to complete the combustion of the gases rising from the grate. Such incompletely burned gases, together with the finer particles of fuel, are directed by the arches 21 and 23 to the narrow passage 24, from which they pass through the narrow passage 24 into the combustion chamber 25, mingling with additional combustion air from the nozzles 28,' this auxiliary or additional combustion air being supplied in suicient quantity to complete the combustion of the gases and fine particles of fuel. By bringing all of these gases and fine particles into a comparatively narrow space, the additional air is thoroughly mixed therewith, so that as these gases expand into the upper combustion chamber 25, the gases and fine particles are substantially completely burned before passing into the gas outlet 27. It will be noted that, by our arrangement, any possible stratification of the gases and air rising from the grate, which stratification occurs in furnaces as heretofore made, is entirely avoided by directing, all of the gases and air passing through the grate into the narrow throat.

By forming the upper combustion chamber' 25 as shown, the gases therein are given a turbulence which completes the mixing of the air and gases, which mixing is aided by the provision of the gas outlet at one side of the upper combustion chamber.

We have found from 'experience with this type of furnace and with the metho-d of operation as described above, that the amount of air supplied can be regulated close to the theoretical amo'unt of air required for the complete combustion of the fuel, without any appreciable amount of excess air. In practically all cases, the quantity of air supplied through the grate is larger than'that supplied through the nozzles 28. Preferably we arrange the dampers in the ducts 38 leading to the spaces beneath the fuel bed so that little or no air passes through the fuel at the front and middle portions of the grate and so that a somewhat larger quantity of air flows through the rear end of the grate, thequantities of air that do pass through the grate being such as to be used up largely in the burning of the solid fuel on the grate. Consequently, the gases which enter the narrow throat 24 are partly unburned combustible gases.

In the narrow throat 24, the unburned gases and the auxiliary combustion air are brought together in a'small space and the subsequent expansion into the upper combustion chamber intimately mixes the two and the combustion is thereby substantially completed. The passing of the gases through the narrow passage 24 between the larger spaces below and above the passage acts like a Venturi tube, so that there is substantially no increase of draft resistance, the pressure, at least under some conditions, being lower' in the passage 24 than it is in the upper andthe lower combustion chambers.

By arranging the roof arch 23 in the manner shown, we have found that a large part of the relatively fine particles of burning fuel that may be carried up from the rear end of the fuel bed by the combustion air supplied beneath it, is thrown forwardly and down on the incoming fuel, thereby aiding the igniting of the fresh fuel, instead of being carried up into the upper combustion chamber, the slope of this arch being arranged to produce this' effect.

We preferably operate the furnace so that the pressure at the narrow passage 24 is negative and thereby avoid too high a heat at this point, which would tend to destroy the arches 21 and 23.

The air ducts 29 and 30 cool the walls surrounding the narrow passage through which the burning gases pass and also serve to support the arches 2l and 23. These arches preferably are suspended Ain a well-known manner on metallic members on which the tile are suspended, these metallic members, in turn, being supported on hangers connected to the ironwork of the ducts 29 and 30. We have found that the cooling effect of the ducts 29 and 30 is s'uch that arches can be maintained over the fuel bed which would otherwise be impossible, and the heat carried away from the walls of the air ducts 29 and 30 by the air is recovered and returned to the furnace.

As is well known, it is advantageous to supply the combustion air in a heated condition, but particularly where this heated air is supplied through a grate, it is necessary, in order not to destroy the grate, to keep the temperature of the heated combustion air below certain limits. On the other hand, in order to complete the combustion of gases, as, for instance, in the upper part of the furnacey 25, it is desirable to have the combustion air heated to as high a degree as possible. In the arrangement which we have illustrated, the temperature of the air supplied Lesa-5,479

, the flue gases as they emerge from the boiler and this produces a temperature too high to be used directly under the grate. In such cases, the temperature ofthis part of the air may be reduced by abstracting some of the heat from this portion of the combustion air by passing this heated air over the feed Water heater or an economizer 45, the feed water being delivered to the drum 13 through the pipe 46. With this arrangement, the air from the heater 34 may be heated to any desired degree, and it Willbe delivered at substantially this high temperature to the nozzles 28. But the portion of this heated airlwhich is delivered beneath the grate will be at a considerably lower temperature by reason of the abstraction of some of its heat by the economizer or feed water heater. It will be understood that the temperature of the air supplied beneath the grate may be reduced to any desired extent by regulating the flow of the water past the heating surface of the water heater or economizer 45 and thereby varying the amount of heat abstracted from the air, such regulation being effected, inl the form illustrated, by by-passing more or less of the feed water through the pipe 47.

In the illustrated arrangement, a dust hopper 40 is arranged below the second pass of the boiler to receive the dust carried through the boiler by the draft, such particles, of course, being thrown out as the gases turn below the baiie 15. rIhis dust may contain a considerable amqurit of. unburned fuel, and it is desirable to return such lunburned fuel to the fuel bed, and this we accomplish, in the illustrative embodiment, by a duct 41 extending from the dust hopper 40 through the arch 23 above the rear of the Stoker 17. Because of the difference in pressure in the dust hopper 40 and above the grate, it is desirable that communication between the two shall be cut oli' except -fwjhen the dust has accumulated in suflicient quantity to be permitted to'fall to the fuel bed and as a means of accomplishing this, we provide in the duct 41 a valve 42,v normally held closed by the Weights 43 but which will open as the dust accumulates thereon vto permit the dust to fall onto the fuel bed.

Instead of the arrangement of the weighted .iiap valvejust described, the arrangement shown in Fig. 2 may be used, in vwhich the vertical portion 41 of the duct 41 is provided With an aspirating tube 44 which may conveniently be supplied with air from the combustion air ducts. This aspirator will draw the line particles from the duct`41 and force them to the lfuel bed.

It will be understood that ne particles accumulating in any part of the system, such, for instance, as any of the overhead flues leading from the boiler or in air heaters or the like, if such air heaters are used, may similarly be conveyed back to the fuel bed.

The arrangement illustrated by which the combustion air is heated directly by the boiler waste gases without reducing the temperature of the gases by an economizer or the like, and then transferring some of the heat to the boiler feed water before supplying the air to the fuel is advantageous irrespective of the particular way in which the air is used. In

such an arrangement, the heating surfaces of the economizers are contacted only with clean and relatively dry air instead of with the dust-laden products of combustion, so that the tubes or the like usually found in economizers are kept free from dust and possible `corrosion from the mixture of the sulphurous gases and the like with moisture on the tubes. It Will be understood that the arrangements which we have shown are merely illustrative and that the embodiment of our invention may be widely varied. It will also be underv stood that certain features of our 'invention may be used with or without other features, as

desired.

We claim: 1. A furnace comprising a lower combustion chamber and an upper combustion and expansion chamber, said chambers being Connected by a restricted throat, the upper chamber flaring upwardly from the throat, a boiler having heat absorbing surfaces disposed in a chamber'communicating with said upper chamber, air ducts on opposite sides of said throat, nozzles communicating with, said ducts and adapted to discharge air therefrom into the furnace adjacent said throat, a progressive feed grate in the bottom of said lower chamber, means to supply fuel vto said grate, and means to supply air to said ducts, burning fuel from said grate passing through said throat into and then through said upper combustion and expansion chamber into contact with said heat absorbing surfaces of the boiler, and said upper combustion and expansion chamber being designed to insure apy proximate completion of combustion of said tional area than said throat transverse to the direction offlow of gases thrughsaid chambers, a boiler having heat absorbing surfaces disposed ina chamber communicating with said upper- "chamber, air ducts on opposite sides of said throat, nozzles communicating withsaid ducts and adapted to discharge air 110 said lower combustion chamber and through therefrom into the furnace adjacent said throat, a progressive feed grate in the bottom .tion chamber and an upper combustion and expansion chamber, said chambers being connected by a restricted throat, the walls of both chambers flaring outwardly from the throat transverse to the direction of flow of gases through said chambers, a boiler having heat absorbing surfaces disposed in a chamber communicating with said upper chamber, air ducts on opposite sides of said throat, nozzles communicating with said ducts and adapted' to discharge air therefrom into the furnace adjacent said throat, a progressive feed grate in the bottom of said lower chamber, means to supply fuel to said grate, and

means to supply air to said ducts, burning fuel from said grate passing through said lower combustion chamber and through said throat into and then through said upper combustion and expansion chamber into Contact with said heat absorbing surfaces of the boiler, and said upper combustion and expansion chamber being designed to insure approximate completion of combustion of said burning fuel as it passes therethrough.

4. A furnace comprising a lower combustion chamber and an upper combustion and expansion chamber, said chambers being connected by a restricted throat, the walls of both chambers flaring outwardly from the throat transversely to the direction of dow of gases through said chambers, the throat being disposed nearer the front of the furnace than the rear, a boiler having heat absorbing surfaces disposed in a chamber communicating with said upper chamber, air ducts on opposite sides of said throat, nozzles communicating with said ducts and adapted to discharge air therefrom into the furnace adjacent said throat, a progressive feed grate in the bottom of said lower chamber, means to'supply fuel to said grate, and means to supply air to said ducts, burning fuel from said grate passing through said lower combustion chamber and through said throat into and then through said upper combustion and expansion chamber into contact with said hcat absorbing surfaces of the boiler, and said upper combustion and expansion chamber being designed to insure ap- Legame roximate completion of combustion of said burning fuel as it passes therethrough.

5. A furnace comprising a lower combustion chamber and an upper combustion and expansion chamber, said chambers being connected by a restricted throat, and each chamber being of substantially greater cross-sectional area than said throat transverse to the direction of flow of gases through said chambers, boiler tubes so located as to be exposed to the expanded hot gases in said upper chamber, air nozzles adapted to discharge air into the furnace adjacent said throat, a progressive feed grate in the bottom of said lower chamber, means to supply fuel to said grate, and means to supply air to said nozzles, burning fuel from said grate passing through said lower combustion chamber and through said f throat into and then through said upper combustion and expansion chamber into contact with said boiler tubes, and said upper combustion and expansion chamber being designed to insure approximate completion of combustion of said burning fuel as it passes therethrough.

6. A furnace comprising a lower combustion chamber and an upper combustion and I expansion chamber, said chambers being connected by a restricted throat and each chamber being of substantially greater cross-sectionall area than said throat transverse to the direction of flow of gases through said chambers, a progressive feed stolzer in the bottom of said lower chamber and adapted to move fuel from the front toward the rear thereof, a relatively short arch extending from said throat to the front wall of the lower chamber, a relatively long arch extending from said throat to the rear wall of the lower chamber, boiler tubes so located as to be exposed to the expanded hot gases discharged from said upper chamber, and means to introduce air into the furnace adjacent said throat, burning fuel from said grate passing through said lower combustion chamber and through said throat into and then through said. upper combustion and expansion chamber into contact with said boiler tubes, and said upper combustion and expansion chamber being designed to insure approximate completion of combustion of said burning fuel as it passes therethrough.

7 A furnace comprising a lower combustion chamber and an upper combustion and expansion chamber connected by a restricted throat, said upper chamber being disposed vertically above said lower chamber and having a greater height than said lower chamber and of greater cross sectional arca than said throat transverse to the direction of flow of gases through said upper chamber, boiler tubes so located as to be contacted by the expanded hot gases in said upper chamber, air nozzles adapted to discharge air into the furnace adjacent said throat, a progressive feed grate in the bottom of said lower chamber, means to supply fuel to said grate, and means to supply air to said nozzles, burning fuel from said grate passing through said lower combustion chamber and through said throat into and then through said upper combustion and expansion chamber into contact with said boiler tubes, and said upper combustion and expansion chamber being designed to insure approximate completion of combustion of said burning fuel as it passes therethrough.

8. A furnace comprising a lower Vcombustion chamber and an upper combustion and expansion chamber, said chambers being connected by a longitudinally restricted throat portion andeach chamber progressively in,- creasing in cross-sectional area from said throat portion in a direction transverse to the flow of gases through said throat portion and chambers, a progressive feed stoker extending longitudinally of said lower chamber and adapted to move fuel from the front toward the rear thereof, a relatively short refractory arch sloping downwardly and forwardly relative to said stoker from said throat portion to the front wall of said lower chamber, a relatively long refractory arch sloping downwardly and rearwardly relative to said Stoker from said throat portion to the rear wall of the lower chamber, refractory walls gradually diverging upwardly from said throat portion and defining said upper chamber, the angle of divergence'of'the walls delining said upper chamber being considerably less than the angle of convergence of the arches of said lower chamber, the length of said throat portion at its most restricted point being not more than 17% of the eii'ective length of said Stoker in said furnace, said upper chamber being proportioned to insure approximate completion of combustion of the burning fuel gases passing thereto, and boiler tubes arranged to receive heat radiated fromone of said walls of said upper chamber.

THOMAS G. COGHLAN. EINAR A1 JOHN SEN. 

